Power line communications (PLC) include systems for communicating data over the same medium (i.e., a wire or conductor) that is also used to transmit electric power to residences, buildings, and other premises. Once deployed, PLC systems may enable a wide array of applications, including, for example, automatic meter reading and load control (i.e., utility-type applications), automotive uses (e.g., charging electric cars), home automation (e.g., controlling appliances, lights, etc.), and/or computer networking (e.g., Internet access), to name only a few.
Current and next generation narrow band PLC are orthogonal frequency division multiplexing (OFDM)-based (as opposed to frequency shift keying (FSK)-based) in order to get higher network throughput. OFDM uses multiple orthogonal subcarriers to transmit data over frequency selective channels. A conventional OFDM structure for a data frame includes a preamble, followed by a physical layer (PHY) header, followed by a data payload. Examples of OFDM-based PLC standards include IEEE P1901.2 and PoweRline Intelligent Metering Evolution (PRIME).
In PLC networks, the system has the ability to communicate in both low voltage (LV) powerlines as well as high voltage power lines. When operating in a high-voltage powerline the system is able to communicate with low-voltage powerlines. This means that the receiver on the LV side must be able to detect the transmitted signal after it has been severely attenuated as a result of going through a medium voltage (MV)/LV transformer. The coupling interface between the PLC device and the MV medium may be referred to as a MV/LV crossing.
In PLC networks that have MV/LV crossings, data transmission over the full FCC allowed frequency band may not be feasible due to network conditions (e.g., noise) so that smaller frequency band portions referred to as tone masks (or subbands) may be needed for each particular MV/LV communication link. A tone map in contrast to a tone mask refers to an allocation of power within a tone mask. The tone mask can thus be considered to be a collection of tone maps.
The receiving PLC device may be “listening” only on one tone mask at a given time. Since the set of tone masks that provide effective communications for a particular link may vary link-to-link, the receiver may not be tuned to the proper set of tone masks to decode the received frame. When nodes are unable to decode the data payload sent over the tone masks indicated in the received frame, such as indicated in the PHY header referred to as the frame control header (FCH) in the case of the IEEE P1901.2 standard, the node will set their virtual carrier sensing (VCS) to the EIFS value to account for the largest data payload size transmission allowed in the network.